A method of heat-bonding interior material

Abstract

 A heat-bonding method for interior material includes heating one electrode of a high-frequency welder. The temperature to which the electrode is heated is generally about 100°C less than the melting point of the outermost interior finishing material. The increased temperature raises the susceptibility of the cushioning material to dielectric heating due to a high-frequency oscillating voltage from the high-frequency welder. There is also disclosed a method for selecting a urethane foam as a cushioning material which is optimal for use with the disclosed heat-bonding method, by determining the specific gravity and the air permeability rate of the urethane foam.

Description

BACKGROUND OF THE INVENTION

1) Field of the Invention

[0001] The present invention relates to a high-frequency heat-bonding method for layers of material used to finish automotive vehicle interiors, including seat cushions. The invention relates more. specifically to a method of heat-bonding foam resin material to outer finishing layers without using adhesives or chemical heat-. bonding agents. Even more specifically, there is disclosed a method for selecting a urethane foam most suitable for use in the method of the present invention.

2) Description of the Prior Art

[0002] In order to finish automotive vehicle interiors, generally, an interior finishing material such as nylon cloth, a cushioning material such as foamed urethane, and a lining material such as nylon cloth, cotton cloth (calico), or non-woven material are piled up in order and heat-bonded to each other at the desired positions. In some cases, however, only a finishing material and foamed resin material are heat-bonded, omitting the lining material.

[0003] Conventionally, in the case where the interior finishing material, a foamed resin material and a lining material are heat-bonded together at the necessary positions, a high-frequency welder has been used to heat . these three materials.

[0004] In the prior-art heat bonding method, however, since the melting temperature of the foamed resin material is higher than that of the interior finishing material, it is difficult to melt only the foamed material without melting the interior finishing material. Further, when these two materials. are heat-bonded without melting the finishing material, it is difficult to heat-bond the layers firmly.

[0005] To overcome this problem, it has been necessary to apply an appropriate heat-bonding agent or adhesive agent, in advance, onto one or both sides of the foamed resin material locally, or to impregnate a powder heat-bonding agent thereinto or liquid adhesive agent thereon for bonding the layers of these materials together.

[0006] In the above-mentioned method in which a heat-bonding agent or an adhesive agent is previously used for the foamed resin cushion, however, in practice it is difficult to apply or impregnate the heat-bonding agent or the adhesive agent correctly to the desired positions, in addition to the extra manufacturing process involved, thus resulting in an increase in manufacturing cost.

[0007] A more detailed description will be made hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.

SUMMARY OF THE INVENTION

[0008] With these problems in mind therefore, it is the primary object of the present invention to provide a method of heat-bonding layers of material used to finish automotive vehicle interiors, without using any adhesives or chemical heat-bonding agents.

[0009] To achieve the above-mentioned object, the method of heat-bonding an interior finishing material and a foamed resin material together firmly comprises the processes of heating the electrodes used for high frequency induction heating to a given temperature previously and selecting the specific gravity and the air permeability rate of the foamed resin material in advance.

[0010] The layers of material pertaining to the present invention include an inner material incorporating a cushioning material, such as foam resins, and an interior finishing material. A high-frequency welder comprises a stationary electrode platen, a movable electrode, means for heating the movable electrode, and a high-frequency AC generator connected between the electrodes for applying high-frequency alternating current thereto. The movable electrode is heated so as to favorably affect the dielectric induction heating characteristics of the cushioning material. When suitably hot, the electrode is lowered so as to pinch the materials to be bonded against the electrode platen, thereby applying the heat of the electrode to the materials. Simultaneously the generator operates to create a high-frequency oscillating voltage across the electrodes with_' the materials acting as a composite dielectric.

[0011] The pre-heating due to the movable electrode affects the dielectric heating characteristics of the different materials to different degrees in such a manner that dielectric heating is increased in the materials with higher melting points. In this manner, the materials can all be brought to near melting without danger of causing melting damage to any of the materials. Thus, strong bonding can be achieved without adversely effecting the appearance of the interior finishing material.

[0012] There are also disclosed criteria for the selection of foam resin, especially urethane foam, suitable for use with the method of the present invention. The presence of large foam cells adversely effects bond strength. Since cell size is inversely proportional to foam density, foam resins of sufficient specific gravity will be nearly free of large cells. Cell size uniformity also implies a lack of large cells. For low-specific-gravity foam resins, air permeability rate is a good indicator of cell size uniformity. Appropriate ranges of specific gravity and/or air permeability are disclosed for urethane foam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The application and advantages of the invention will be easily discerned by reference to the detailed description of the preferred embodiment and the following drawings, wherein:

_Fig. 1 is a diagram of a prior-art heat-bonding operation;

_Fig. 2 is a cross-sectional view of interior material including a heat bond produced by the method of Fig. 1; .

Fig. 3(a) is a perspective view of an automotive seat depicting a prior-art wrinkle-reduction method;

Fig. 3(b) is an enlarged perspective view of the wrinkled area labeled 'b' in Fig. 3(a);

_Fig. 3(c) shows the area of Fig. 3(b) after application of the wrinkle-reduction method depicted in Fig. 3(a);

Fig. 4 is a cross-sectional view of a bonding site which has failed due to application of the wrinkle-reduction method of Fig. 3(a);

Fig. 5 is a diagram of a preferred embodiment of the method of the present invention; and

Fig. 6 is a cross-sectional view of a bonding site as produced by the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] To facilitate understanding of the present invention, a brief reference will be made to a prior-art method of heat-bonding layers of automotive vehicle interior materials, with. reference to the attached drawings.

[0015] The material used to cover automobile interior surfaces and seats generally includes an interior finishing material, such as nylon cloth, polyamide resins, and many others, underlaid with a cushioning material, such as urethane foam resins, and a lining material such as nylon or cotton cloth (calico) or a non-woven material. In some cases, the lining material is omitted. Frequently, these layers are'heat-bonded together at specified positions to form seams, pleats, tucks, recesses, and the like. This heat bonding is performed by a high-frequency welder as shown in Fig. 1 which comprises a stationary electrode platen 16, a vertically-movable electrode 14, and a high-frequency AC generator 18 connected between the two electrodes for providing high-frequency alternating current thereto on demand.

[0016] A layer of interior finishing material 12, cushioning material 11, and lining material 10 are vertically ordered and horizontal aligned as desired on the electrode platen 16. The movable electrode 14 is then lowered toward the stationary electrode platen 16 so as to pinch the layers of material 10-12 together between the electrodes 14 and 16. The high-frequency AC generator 18 then operates to generate a high-frequency oscillating voltage across the electrodes 14 and 16 with the layers of material 10-12 acting as a composite dielectric. Brief application of the high-frequency oscillating voltage raises the temperatures of the material layers 10-12 to . near melting due to dielectric induction heating. Due to the pinching pressure, the softened material layers 10-12 partially coalesce at the spot A (in Fig. 2) between the electrodes 14 and 16. The electrode 14 is then removed from the spot A, and the material layers cool and harden to form a bonding site at.the spot A, as shown in Fig. 2.

[0017] The strength of the heat bond depends critically on how close to melting the material layers come before solidifying to form the bonding site. However, since the melting temperature of the foam resin material (about 250°C) tends to be higher than that of the interior- finishing material (about 220°C), it is difficult to achieve strong bonding without melting the finishing material.

[0018] Therefore, there exists a method of impregnating a heat-bonding agent with a melting point of about 150°C into a given part of the foamed urethane cushioning material 11 as shown in Fig. 1 by the hatched area P. In this method, after the above treatment has been completed, pressure is applied to the three layers of interior finishing material 12, foamed urethane cushioning material 11 and lining material 10 by the movable electrode 14 and then a high frequency voltage is applied thereto by the high frequency welder 18, so that the desired position A is heat-bonded, as depicted in Fig. 2.

[0019] On the other hand, there readily appear wrinkles 7 on uneven positions. To remove these wrinkles 7, it is effective to blow steam with a vapor pressure of 4-6 _Kg/c_m² and vapor temperature of 140-160°C against the seat cover by inserting a blowing nozzle 8 under the seat cover in order to remove the wrinkles completely as shown in Fig. 3(C).

[0020] In this wrinkle-reduction process, however, since the temperature of the applied steam is comparable to the melting point of the heat-bonding or adhesive agent, seat covers previously heat-bonded are susceptible to deformation and therefore the complete failure of the bond can occur as shown in Fig. 4. This may be due to the fact that since the sizes of the cells within the foamed resin material are not uniform, there may be some places where it is impossible to heat-bond the materials together firmly by using high frequency induction heating.

[0021] In general, the greater the specific gravity of foamed resin material, the more uniform will be the size of the foamed cells. In contrast with this, the smaller the specific gravity of foamed resin material, the less uniform will be the size of the foamed cells. Therefore, it is desirable to use a foamed resin material of a large specific gravity for stabilization of the heat-bonding, however, the greater the specific gravity, the higher the cost thereof, it is thus desirable to use a foamed resin material of a smaller specific gravity, that is, of a lower cost for mass-producing foamed resin cushions.

[0022] One well-known way of dealing with this problem is to apply adhesives or chemical heat-bonding agents to the foam resin at the bonding site, as shown in Figs. 1 and 2 by the cross-hatched area P. This provides a strong bond, but incurs added costs in materials and application of labor.

[0023] In view of the above description, reference is now made to Figs. 5 and 6, and more specifically to Fig. 5, for explaining a method of heat-bonding the interior finishing material and foamed resin material according to the present invention.

[0024] In these figures, reference numeral 10 denotes a lining material, numeral 11 denotes a foamed urethane cushioning material the specific gravity and the air permeability rate of which are pre-selected. In this embodiment, nylon is used for the lining material, and urethane with a specific gravity of 0.021 and an air permeability rate of 80-250 cc/cm².sec (for a thickness of 1 cm) is used for the foamed finishing material.

[0025] Reference numeral 12 denotes the interior finishing material. In this embodiment, it is possible to use various materials such as stockinette, vinyl leather, etc., without limiting the interior finishing material to polyamide resin, since no heat-bonding agent or adhesive agent liable to produce stains or spots on the. finishing material is necessary for heat-bonding it to the foamed urethane cushioning material 11, since this method is different from the prior-art method. Further, in this . embodiment, it is also possible to use urethane onto which cloth woven from nylon yarn is bonded. That is to say, according to the present invention, it is possible to use various kinds of interior finishing materials according to their use, an improvement on the conventional method.

[0026] In Fig. 5, reference numeral 16 denotes a stationary electrode platen, numeral 14 denotes a movable electrode disposed against the electrode plate 16, and numeral 18 denotes a high frequency AC generator.

[0027] For the electrode 14, a heating means such as an electric heater 13 is provided. Additionally, a temperature sensor 15 is disposed in a position so as to keep the electrode temperature at a constant temperature of, for instance, 100°C lower than the melting point of the interior finishing material 12 when the interior finishing material and foamed resin material are heat-bonded together.

[0028] The shape of the movable electrode 14 is selectable according to the use, for example, such as the use for the seat, door, etc. In this embodiment, a 2 mm- wide, 600 mm-long (perpendicular to the paper in Fig. 5) electrode is used.

[0029] In the system of the preferred embodiment of the invention shown in Fig. 5, a layer of cushioning material 11, such as urethane foam, is sandwiched between layers of lining material 10, such as nylon cloth, and interior finishing material 12, such as decorative nylon cloth or non-woven polyamide resin. The arranged layers rest on a stationary electrode platen 16 of a high-frequency welder 18. The other movable electrode 14 of the high-frequency welder 18 is provided with heating devices 13, such as resistive heating coils. The heating devices 13 serve to heat the electrode 14, preferably to a temperature of the. order of 100°C below the melting temperature of the interior finishing material 12.

[0030] When the electrode 14 is adequately hot, it is lowered toward the electrode platen 16 so that it provides some pinching pressure to the layers of material 10-12 at the desired bonding site A as shown in Fig. 6. At that time, the high-frequency welder 18 generates a high-frequency oscillating voltage between the movable electrode 14 and the stationary electrode platen 16 with the material layers 10-12 acting as a composite dielectric.

[0031] Dielectric induction heating due to the oscillating electric field and direct heating from the heated electrode 14 cause a momentary increase in plasticity of the material layers (10-12) so that they partially coalesce due to the pinching pressure. When the layers 10-12 cool after removal of the electrodes 14, 16, they remain partially united at the pinched portion A to form a bonding site.

[0032] In this embodiment, since the movable electrode 14 is separated from the interior finishing material 12 immediately after the heat-bonding has been completed, it is possible to obtain a strong heat bonding at any desired position as shown by the symbol A in Fig. 6 without any damage to the interior finishing material 12 and the lining material 10 due to overheating.

[0033] The reason why a good heat-bonding result can be obtained without special previous treatment of applying an adhesive agent onto .or impregnating a heat-bonding agent into the foamed urethane cushioning material can be explained as follows:

Generally, the heat P (in W/cm³) generated in a dielectric material by dielectric heating can be expressed as follows:

where f: oscillation frequency

_E: dielectric constant

E: electric field intensity

tan 6: dielectric power factor

[0034] In the above expression, it is possible to increase the strength of heat bonding by increasing the heat P. Although it is desirable to increase the electric power applied to the materials in order to increase the electric field intensity E, when the power is excessively large, there is a problem such that a spark is easily generated. Also, at present, three oscillation frequencies f of 13.56 MHz, 27.12 MHz and 40.68 MHz are used for the industrial use.

[0035] In the above expression, the dielectric constant ε is roughly the same in each material, and the dielectric power factor tan 6 changes according to each material and material temperature. Therefore, in this embodiment according to the present invention, since the movable electrode 14 is heated to 80-120°C previously by the electric heater 13 to heat the foamed urethane cushioning material 11 partially by transmitting heat directly to the foamed urethane cushioning material 11 through the interior finishing material 12 when a pressure applied thereto, it is possible to increase the dielectric power factor, that is, to increase the internal heat generated.

[0036] In this case, although the interior finishing material 12 is also heated because the movable electrode 14 is in contact therewith, the interior finishing material does not melt. This is because the increase in dielectric power factor of the interior finishing material 12 due to heating is smaller than that of the dielectric power factor of the foamed urethane cushioning material 11 due to heating.

[0037] According to experiments, it is possible to obtain a good result, without paying special attention to the air permeability rate, when the specific gravity of the foamed urethane cushion is above 0.022. In this embodiment, however, a good result from the standpoint of economic considerations has been obtained by using a foamed urethane of specific gravity of 0.021 or less or by using a foamed urethane with an air permeability rate of ₈₀- ₂₅0 cc/cm² sec with a thickness of 1 cm when the specific gravity thereof is 0.021.

[0038] In this connection, in this method of heat-bonding the interior finishing material to the foamed urethane according to the present invention, a good result has been obtained when the oscillation frequency is 40.68 MHz, and the size of the electrode plate 4 is (1000-1500) mm in length and (800-1000) mm in breadth.

[0039] As described hereinabove, according to the present invention, since it is unnecessary to apply an adhesive agent onto or impregnate a heat-bonding agent into the foamed resin material, it is possible to prevent the heat-bonded positions from being separated from each other even when high-temperature, high-pressure steam is blown against the interior finishing material to remove wrinkles produced thereon specially when the material is used for the seat cover of vehicle seats, in addition to reducing the number of manufacturing processes and the manufacturing cost markedly.

[0040] Furthermore, since various kinds of interior finishing materials are usable because no heat-bonding agent or adhesive agent is applied thereto, it is possible to select a desirable material from among various interior finishing materials taking into consideration the . appearance and feel of the material.

[0041] The method of the present invention can be seen to provide several advantages. Avoiding the use of chemical adhesives or heat-bonding agents saves time and money in manufacturing and allows for selection of cushioning and interior finishing materials from a wider range of possibilities. The invention also provides for the use of low-specific-gravity urethane foam as a cushioning material, which also reduces material costs. These advantages are in addition to the basic advantage of providing a strong and reliable bond.

[0042] It will be understood by those skilled in the art that the foregoing description is in terms of preferred embodiments of the present invention wherein various changes and modifications may be made without departing from the spirit and scope of the invention, as is set forth in the appended claims.

Claims

1. A method of heat-bonding interior materials comprising the following steps of:

(a) arranging a layer of interior finishing material and a layer of foamed resin cushioning material to be bonded;

(b) heating the electrode of a high-frequency welder to a temperature below the melting point of the outermost layer of the interior materials to be bonded;

(c) pinching the layers of the interior materials to be bonded between the heated electrode and the opposing electrode platen of the high frequency welder; and

(d) applying a high frequency oscillating voltage between the two electrodes,

-whereby the interior materials can be heat-bonded without using any adhesive agent or heat-bonding agent.

2. A method of heat-bonding interior materials as set forth in claim 1, which further comprising a step of selecting, in advance, a foamed resin cushioning material having foam of nearly uniform cell size, whereby a uniform heat-bond force is obtained, even after high-temperature, high-pressure steam is blown against the interior finishing material to move wrinkles produced thereon.

3. A method of heat-bonding interior materials as . set forth in claim 2, wherein a foamed resin cushioning material having foam of nearly uniform cell size is selected, in advance, in accordance with its specific gravity being within a predetermined range.

4. A method of heat-bonding interior materials as set forth in claim 3, wherein the foamed resin cushioning material having form of nearly uniform cell size is further selected, in advance, in accordance with its air permeability rate being within a predetermined range.

₅. A method of heat-bonding interior materials as set forth in claim 1, wherein the interior finishing material is polyamide resin.

6. A method of heat-bonding interior materials as set forth in claim 1, wherein the interior finishing material is stockinette.

7. A method of heat-bonding interior materials as set forth in claim 1, wherein the interior finishing material is vinyl leather.

8. A method of heat-bonding interior materials as set in claim 1, wherein the interior finishing material is urethane onto which a nylon woven cloth is laminated.

.9. A method of heat-bonding interior materials as set forth in claim 1 wherein the foamed resin cushioning material is foamed urethane.

10. A method of heat-bonding interior materials as set forth in claim 1, wherein said arranging interior materials further comprises the step of arranging a layer of lining material in addition to the layer of interior finishing material and the layer of foamed resin cushioning material.

ll. A method of heat-bonding interior materials as set forth in claim 10, wherein the lining material is nylon cloth.

12. A method of heat-bonding interior materials as set forth in claim 10, wherein the lining material is cotton cloth or calico.

13. A method of heat-bonding interior materials as set forth in claim 3, wherein a predetermined range of specific gravities is 0.022 or more.

14. A method of heat-bonding interior materials as set forth in claim 4, wherein the predetermined range of specific gravities is 0.021 or less and the predetermined. range of air permeability rate is from 80 to 250 cc/cm².sec with a thickness of 1 cm.

15. A method of heat-bonding interior materials as set forth in claim 1, wherein the electrode of the high-frequency welder is heated to 80 to 120°C, in the case when the melting point of the interior finishing material is 220°C and that of the foamed resin cushioning material is 250°C.

16. A method of heat-bonding interior materials as set forth in claim 1, wherein the size of the electrode of the high-frequency welder is about 600 mm long and about 2 mm broad.

17. A method of heat-bonding interior materials as set forth in claim 1, wherein the size of the electrode platen of the high-frequency welder is 1000-1500 mm long and 800-1000 mm broad.

18. A method of heating-bonding interior materials as set forth in claim 1, wherein the frequency of the oscillating voltage is in the range of about 10 MHz to 50 MHz.

Drawing